I. Field
The following description relates generally to wireless communications systems and more particularly to control signals.
II. Background
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
Within a wireless communication system physical channels are normally further divided into dedicated channels and common channels depending on the entities being serviced. A dedicated channel is assigned to facilitating communications between a base station and a specific UE. A common channel is shared by different UEs and is used by a base station to transmit signals that are commonly communicated to all users within the geographic area (cell) being serviced by the base station. According to LTE technology, all allocations are signaled in Shared Control Channels, which are coded separately. Hence, a downlink (or uplink) channel is divided into two separate parts, one for each of control and data messages. The data part (PDSCH—Physical Downlink Shared Channel) carries downlink (or uplink) data for simultaneously scheduled users, while the control part (PDCCH) carries (among others) allocation information for scheduled users. Hence, reliable exchange of control signals is necessary for implementing efficient wireless communication systems.